I9H.] STEVEXSOX— FORMATIOX OF COAL BEDS. 45 



They were deposited in shallow water, for they are close to coal beds 

 and show the shrinkage cracks due to drying. 



Andrews adheres to the doctrine of accumulation /;/ situ, assert- 

 ing that his studies leave no room for any other conclusion. The 

 vegetation grew on marshy plains skirting the ocean or perhaps 

 making low islands near the shore. Slates as coal partings are of 

 great geographical extent, holding the same stratigraphical position 

 throughout, thus implying a temporary overflow of the marsh by 

 ocean waters, with an even distribution of the sediment. Some beds 

 contain evidence of tidal flows, for beachworn sticks, replaced by 

 pyrite, lie in the coal as they were drifted upon the marsh. After 

 complete submergence of the bog, trees growing on the surface were 

 overthrown by turbulent waters ; thousands of trunks of Pccoptcris 

 arborcsccns are seen in the roof of the Pomeroy coal bed, bent or 

 broken down by the sediment-carrying water ; and with them are 

 great trunks of Sigillaria and Lcf^idodciidroii : while, in sandstone, 

 drifted and buried trees from upland areas are not rare. The con- 

 tinuity of coal seams was often interrupted, as should be expected in 

 great areas. 



Andrews's studies were confined chiefly to southeastern Ohio and 

 the adjacent portions of West A'irginia, where the coal area ap- 

 proaches the central part of the basin, the original western border 

 having been many miles beyond the present western limit of the Coal 

 ?\Ieasures. The irregularities of deposit are comparativelv insigni- 

 ficant and the important members show a remarkable parallelism. 

 He was led by the phenomena of his region to deny the possibility of 

 notable variations in thickness of intervals between coal beds and he 

 refused to accept as correct the great variations reported from the 

 anthracite areas. 



There are many evidences of erosion and planation during deposi- 

 tion of sandstones. The great bed on Sunday creek shows erosion 

 from one foot to entire thickness of the bed, the overlying sandstone 

 filling the trench and resting unconformably on the eroded edges of 

 the coal. The eroded surface is smooth, there being no traces of 

 rough work such as one should expect to find, if the coal were still 

 soft and unconsolidated at the time of removal. 



45 



